MESOSCALE PRECIPITATION DISCUSSION 0398
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1248 PM EDT THU JUN 30 2016
 
AREAS AFFECTED...NORTHWEST AZ & SOUTHWEST UT 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 301647Z - 302247Z
 
SUMMARY...THUNDERSTORMS ARE BEGINNING TO DEVELOP ACROSS
WEST-CENTRAL AZ.  OVER THE NEXT SEVERAL HOURS, HOURLY RAIN RATES
UP TO 2" COULD LEAD TO FLASH FLOODING/DEBRIS FLOWS.

DISCUSSION...AN UPPER LEVEL DISTURBANCE IS SLOWLY MOVING EASTWARD
ACROSS NV TOWARDS UT AT THE PRESENT TIME PER WATER VAPOR IMAGERY,
WHICH APPEARS TO BE ENHANCING DIVERGENCE ALOFT ACROSS THE MPD
AREA.  INFLOW AT 700 HPA IS CONVERGENT ACROSS THE REGION, WITH
SPEEDS OF AROUND 15 KTS PER VAD WIND PROFILES, CLOSE TO THE
MAGNITUDE OF THE 850-250 HPA MEAN WIND -- THE FLOW IS
UNIDIRECTIONAL WITH HEIGHT. PRECIPITABLE WATER VALUES ARE
0.8"-1.25", WHICH IS 3-4 SIGMAS ABOVE THE MEAN/NEAR RECORD VALUES
FOR LATE JUNE AND WOULD EQUATE TO >1.5" AT SEA LEVEL.  CIN IS
BEGINNING TO ERODE, AND SHOULD BE ELIMINATED BY 20Z PER RAP
FORECASTS.  MLCAPES OF UP TO 2000 J/KG EXIST IN THE AREA PER SPC
MESOANALYSES.  SUNNY SKIES HAVE ALLOWED NEW THUNDERSTORM ACTIVITY
TO DEVELOP PER RECENT RADAR AND SATELLITE IMAGERY.

THE EXPECTATION IS FOR THUNDERSTORMS TO BECOME SCATTERED IN
COVERAGE DURING THE AFTERNOON HOURS PER RISING GALVEZ-DAVISON
INSTABILITY INDEX VALUES, WHILE MLCAPES ATTEMPT TO RISE TO 3000
J/KG.  CELL TRAINING/MERGERS APPEAR TO BE THE MAIN CULPRITS FOR
HEAVY RAINFALL THIS AFTERNOON.  SOME PROGRESSION TO CONVECTION IN
UT IS POSSIBLE AT THE 700 HPA TROUGH SLOWLY MOVES EASTWARD. 
HOURLY RAIN RATES UP TO 2" ARE EXPECTED WITHIN THIS MOIST AIR
MASS, WITH LOCAL AMOUNTS IN THE 2-4" RANGE POSSIBLE, WHICH IS
GENERALLY SUPPORTED BY THE AVAILABLE MESOSCALE/CAM GUIDANCE.  IF
REALIZED, THIS WOULD REACH THE 100 YEAR RECURRENCE INTERVAL FOR A
SIX HOUR PERIOD FOR SOUTHWEST UT/NORTHWEST AZ.  THE 06Z SSEO
NEIGHBORHOOD PROBABILITIES SUGGEST THE HEAVY RAIN THREAT MAXIMIZES
IN THE 19-22Z TIME FRAME.

ROTH

ATTN...WFO...FGZ...GJT...SLC...VEF...

ATTN...RFC...CBRFC...

LAT...LON   39231187 39221120 38521092 38071033 37201051 
            36151107 35231160 34491287 34351327 34401420 
            35201454 36611391 37291396 38071310 38921241